In recent years, a hybrid vehicle with an engine and a motor, which travels by motive power of at least either one of the engine and the motor, is known. In such a hybrid vehicle, improvement in fuel efficiency is provided by switching two modes based on the operational state of the vehicle: an engine travel mode in which the travel is mainly performed by motive power of the engine; and a motor travel mode in which the travel is performed only by motive power of the motor (also referred to as a motor travel or an EV (Electric Vehicle) travel hereinafter). Furthermore, there exists a vehicle, as a hybrid vehicle, provided with a control device for performing a travel in which at least either one of the vehicle speed and the distance between two vehicles is automatically kept constant (also referred to as a cruise travel hereinafter) when operated by a driver. The technique with respect to control of a hybrid vehicle allowing such a cruise travel is disclosed in, for example, Japanese Patent Laying-Open No. 2005-133682.
The control device disclosed in Japanese Patent Laying-Open No. 2005-133682 controls the hybrid vehicle that can utilize either one or both of engine power and motor power as driving force of the vehicle and is provided with a generator driven by the engine and a battery charged by the generator and serving as a driving source of the motor, such that the vehicle travels at a fixed speed. This control device includes a setting unit for setting a target vehicle speed of the vehicle by operation of a driver during the travel, a motor power control unit for controlling engine power and motor power to perform a fixed-speed travel at the target vehicle speed, an idle stop unit for performing an engine idle stop when the vehicle stops and the driving force is small, and an amount of charge of a battery is not less than a predetermined value, and an engine start-up unit for prohibiting the idle stop when the target vehicle speed is set during the travel by engine power, and for releasing the idle stop and starting up the engine when the target vehicle speed is set during the travel only by motor power.
According to the control device disclosed in Japanese Patent Laying-Open No. 2005-133682, the idle stop is prohibited and the engine is driven during the fixed-speed travel control, even if the vehicle speed is in a region in which the travel by motor power is allowed and the amount of charge of the battery is sufficient for performing the idle stop. Therefore, a situation where starting up and shutdown of the engine are repeated according to varying amount of charge of the battery, regardless of the driver's intention, and a shock is caused can be prevented.
Moreover, Japanese Patent Laying-Open No. 2003-333705 discloses a hybrid vehicle provided with an EV travel switch for enabling an EV travel by operation of a driver of the vehicle.
According to the hybrid vehicle disclosed in Japanese Patent Laying-Open No. 2003-333705, turning on the EV travel switch (EV switch) by the driver switches the vehicle to a mode in which the EV travel is compulsorily performed. This allows the driver to compulsorily stop the engine, by his/her own intention, and to drive the vehicle only by motive power of the motor, even when the vehicle is in a state where the engine should normally operate.
As described above, the control device disclosed in Japanese Patent Laying-Open No. 2005-133682 releases the idle stop and starts up the engine when a target vehicle speed for performing the fixed-speed travel (cruise travel) is set by the driver during the travel only by motor power (motor travel). However, the control device disclosed in Japanese Patent Laying-Open No. 2005-133682 is not provided with an EV switch. Therefore, no reference is made, in Japanese Patent Laying-Open No. 2005-133682, to the control in a case where the driver turns on both the EV switch and the cruise switch. Moreover, in Japanese Patent Laying-Open No. 2003-333705, the EV switch and the control in a case where the driver turns on the EV switch are disclosed while no cruise switch is provided. Therefore, no reference is made, in Japanese Patent Laying-Open No. 2003-333705, to the control in a case where the driver turns on both the EV switch and the cruise switch, as in Japanese Patent Laying-Open No. 2005-133682.